At present, the excimer lasers are considered to be best candidates for light sources for photolithography, and are predominant working light sources in the Integrated Circuit (IC) photolithography industry.
The current excimer lasers have been developed from an original single cavity structure to a dual cavity structure so as to implement a narrower line width and a higher average output power. Those excimer lasers with a dual cavity structure are constituted of two discharge cavities, the configurations of which are substantial identical to each other and are referred to as a seed cavity and an amplifier cavity, respectively. A basic working process is shown as follows: the seed cavity generates a seed light with a narrow line width and a lower energy at a certain repetition rate; the seed light is implanted into the amplifier cavity to be amplified; and a perfect excimer laser with a narrow line width and a high power is output eventually.
A conventional dual-cavity excimer laser is shown in FIG. 1, which is constituted of two discharge cavities 101 and 102, i.e. the seed cavity 101 and the amplifier cavity 102. The two discharge cavities have a pair of discharge electrodes 103 and 104, respectively. There is a module 105 for narrowing the line width at a reflecting end of the seed cavity. The seed cavity 101 and the amplifier cavity 102 are connected by modules 106, 107 and 108 and the functions of these modules comprise control, adjustment and measurement of light path. Such a dual-cavity excimer laser needs to provide the two discharge cavities with a set of high voltage power supplies 109 and 110, respectively.
Some researchers propose an excimer laser with a single-cavity dual-electrode configuration, in which two pairs of discharge electrodes are installed in parallel in one discharge cavity; one pair of the electrodes is configured to generate a seed light and the other pair of the electrodes is configured to amplify the seed light. The advantage of such a technical solution is to facilitate a synchronously control of the discharge and to decrease the complexity of the excimer laser.
A conventional dual-electrode discharge cavity is shown in FIG. 2. Two pairs of electrodes 202 and 203 are installed in parallel in a discharge cavity 201. The two pairs of electrodes only utilize one set of high voltage power supply 204 to discharge. Thus, the complexity of the excimer layer is decreased and the integration of the whole machine is facilitated.
However, it should be noted that when the excimer laser is operated at a high repetition rate, it needs to form a high speed gas flow between the discharge electrodes so as to carry away exhaust gas which has been discharged and to continuously supply fresh working gas for discharge, which guarantees discharge quality and improves energy and reliability of the laser. When the two pairs of electrodes are installed in parallel in the discharge cavity, a gas flow with approximately the same flow velocity and uniformity needs to be generated between the two respective electrodes. Thus, it is desired to design a novel discharge cavity to establish a new means for cycling the gas.